Nucleotide sequence and structure of the Klebsiella pneumoniae pqq operon

A 6940 bp Klebsiella pneumoniae chromosomal DNA fragment, containing genes involved in pyrroloquinoline quinone (PQQ) biosynthesis, was sequenced. Six open reading frames, pqqA, pqqB, pqqC, pqqD, pqqE and pqqF were identified in the pqq operon, which coded for polypeptides of 2764 (23 amino acids), 33,464, 28,986, 10,436, 42,881 and 83,616 Da, respectively. The transcription startpoint was mapped by primer extension analysis, upstream of pqqA, and promoter boxes could be identified. The gene products of pqqB, pqqC, pqqE and pqqF were detected in maxi-cells and the molecular weights of the proteins corresponded with the molecular weights deduced from the nucleotide sequence. The gene products of pqqA, pqqB, pqqC, pqqD and pqqE show 49%-64% identity in amino acid sequence with those of pqqIV, pqqV, pqqI, pqqII and pqqIII respectively in the cloned pqq cluster of Acinetobacter calcoaceticus. The 84 kDa protein encoded by pqqF, which is not present in the cloned pqq cluster of A. calcoaceticus but which is essential for PQQ biosynthesis in K. pneumoniae and Escherichia coli, seems to belong to a family of proteases.